If you mostly use chat-based AI and you're just starting to track new tools, this is the part that matters. You see another AI design post, almost scroll past it, then stop because you do not want to miss the one detail that could change what you try next. The easy mistake is to judge the whole thing by the canvas. The more useful read is simpler: DESIGN.md is turning design rules into agent assets.
Why does that matter? Because if you only watch the surface demo, you can waste time, budget, and attention in the wrong place. The hidden cost is worse: you keep chasing prettier outputs while missing the deeper shift in workflow. A product update is worth checking not by how many features it lists, but by whether it changes your next decision.
That is the key evidence here. Google describes DESIGN.md as an "agent-friendly markdown file" that can move design rules between design and coding tools [S001]. In plain English, your colors, typography, and spacing can travel as instructions the tool can reuse instead of sitting off to the side as notes. The Stitch SDK also exposes uploadDesignMd() and createDesignSystemFromDesignMd() [S003]. That makes DESIGN.md look less like documentation and more like the input for a reusable style system.
So the contrarian takeaway is not 'this tool draws faster.' It is 'the rules are becoming portable.' They are not just selling a canvas; they are turning design rules into something an agent can carry. That does not prove DESIGN.md is the only moat, and it does not make the canvas or agent experience irrelevant. It does mean the smarter question is no longer 'Can it mock up a screen?' but 'Can it carry my rules forward?' Checked against the public Stitch blog and toolkit as of June 2026. Share this with someone still judging AI design tools only by what shows up on the screen.